Thermostatic instrument



(No Model.)

MARTIN. THERMOSTATIG INSTRUMENT.

No. 544,363. Patented Aug. 13,1895.

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UNITED STATES PATENT OFFICE.

'MORRIS MARTIN, OF MALDEN, MASSACHUSETTS.

' I'HERMOSTATIC INSTRUMENT.

SPECIFICATION forming part of Letters Patent N0. 544,363, dated August13, 1895.-

Applieation filed June 5, 1893. Serial No. 476,609- (No model.)

dust and corrosion in the normal or inactive condition of the instrumentand are exposed to the'direct action of the heat when in operation,thereby rendering instruments of this class more sensitive and reliable.The terminals referred to in thermostats of this class as now commonlyconstructed are inclosed in or concealed by a hood secured to the baseof the instrument to prevent it being accidentally detached therefrom,and the said hood is now commonly made whole orsolid, withoutperforations or openings, to protect the contact members or terminals ofthe instrument from dust, corrusion, (he. The hood referred to has beenprovided with small perforations or holes to permit of the passage ofheat to the inexpansible member of the thermostat, but in practice thisconstruction has been found objectionable on account of the liability ofthe holes being closed, as when the ceiling of the room is whitewashedor painted, and because the holes, if not accidentally closed, permit ofthe entrance of dust into the hood, which collects on the terminals ofthe instrument and thereby prevents the electric circuit being closedwhen the instrument is operated by a rise in temperature, as by thebreaking out of a fire.

In accordance with my present invention, the thermostatic instrument isprovided with a hood-passively connected to the instrument, as will bedescribed, and normally inclosing and protecting the active terminal ofthe instrument,'but which is rendered active to expose the saidterminals by a rise in temperature. The hood is preferably composed oftwo parts or members, one part of which is firmly secured to theinstrument and the other part of which is secured to the first part,preferably by a fusible connection or material. The stationary part ormember of the hood is preferably provided with a substantially largeopening, normally closed by the movable part or member, preferably madeas a plate or disk. The plate or movable member of the hood whensubjected to heat is released from the main or stationary portion of thehood, as will be described, and exposes the contact members Within theshell to the direct action of the heat, thereby rendering this class ofinstruments more sensitive and reliable in action.

The particular features in which my invention consists will be pointedout in the claims at the end of this specification.

Figure l is an under side View of a thermostatic instrument embodying myinvention, showing the same as ready to be placed in operative position;Fig. 2, an under side view of the instrument shown in Fig. 1 with theplate or movable'member of the hood removed; and Fig. 3 a sectionaldetail, to be referred to.

The thermostatic instrument herein shown consists essentially of anexpanding member a of any usual or well-known construction, preferablytwo metal strips having diderent rates of expansion, and a contact screwor terminal ct, with which the expanding member a co-operates when actedupon by heat.

The expanding member a is shown as secured to a metal post a and theterminal a is also secured to a metal post a both of which are supportedby a metal plate a, secured, as by screws (1 to a base or support a ofinsulating material, the metal posts a a being insulated from the platea and the latter being provided with arms a 0. through which areextended binding-posts a a, insulated from the plate a and electricallyconnected to the posts a a respectively. The thermostat just describedisand may be of the well-known form and construction now commonly usedon the Well-known Watkins automatic firealarm system.

In accordance with my present invention the contact members a a arenormally protected from dust, corrosion, &c., by a hood, preferablycomposed of two parts b b, which may be of the construction hereinshown.

The part b is herein shown asasubstantially annular rim or ring havingdiametically-oppositc notches b b to fit over the arm a a of the platea. The part b is herein shown as a disk or circular plate having anannular flange or lip 12 which projects beyond or overlaps the edge ofthe openingin the rim or ring I), and is removably secured to said rimor ring by fusible materialsuch as solder, Wax, the. (Indicated in Fig.3 by the heavy black line U.) The opening in the ring or rim 1') ispreferably made substantially large, so that when uncovered by the plateor disk 11 a substantially large inlet is altorded for the passage ofheated air to the contact member or terminal a.

In the normal or inactive condition of the instrument the movable memberof the hood is secured to the stationary member by the fusible material,and the contact members a a are protected from dust, moisture, &c.; butwhen the temperature of the vicinity in which the instrument is placedrises above a certain or predetermined point the fusible material meltsand permits the movable member to uncover the stationary member, thusexposing the expanding member a to the direct action of the heat, thesaid movable member in the present instance acting by gravity to uncoverthe opening in the stationary member of the cover.

My improved instrument enables the contact members or terminals to bethoroughly protected from dust, dirt, moisture, &1'C., when placed inoperative position, and yet enables the instrument to respond to asubstantially low temperature, as the active member of the thermostat isexposed to the direct action of the heatafter it has risen to apredetermined point. I prefer to construct the hood substantially asherein shown, but I do not desire to limit my invention inthis respect,as it is evident the hood may be made of other forms and constructionswithout departing from the spirit of my invention. For instance, thehood may be made in one piece, as now commonly constructed, and held inplace by a fusible material. Furthermore, I do not desire to limit myinvention to the use of a fusible material,

as the hood may be made of material expansible by heat and adapted at anormal tenr perature to cover the instrument, but at an abnormaltemperature to expand and uncover the instrument, the expansion of thehood exposing the active terminal of the instrument to the direct actionof heat.

It will be noticed that the hood for the instrument fits over andincloses, but does not form part of the instrument,anddoes not operateany part of the said instrument, but protects the instrument in themanner above set forth, and is passively connected thereto. The hood,while protecting the instrument from dust, &c., as described, is actedupon by the heat to expose the instrument to the action of the heat, andtherefore can be used with any form of thermostat which is constructedin such manner as to be liable to be rendered inoperative or defectiveby dust, paint, whitewash, dzc.

I claim- 1. The combination with a thermostatic instrument, of aprotective hood inclosing the instrument and passively oo-operatingtherewith and responsive to a rise in temperature to expose the saidinstrument without directly etlfecting the operation of the same, forthe purpose specified.

2. The combination with a thermostatic in strument, of a protective hoodindependent of and disconnected from the active parts of the saidinstrument but normallycovering the same, and a fusible material tosecure the said hood in operative position and operated by heat topermit the hood to expose the active parts of the said instrumentwithout directly effecting the operation of the same, for the purposespecified.

3. The combination with a thermostatic instrument, of a protective hoodinclosing the said instrument and passively cooperating therewith, thesaid hood having a movable member rendered active by an increase intemperature to expose the instrument to the action of heat but not tooperate the same, substantially as described.

t. The combination with a thermostatic instrument, of a protective hoodinclosing the said instrument and having a movable member independent ofthe thermostatic instrument and capable of movement without operatingthe said instrument, and a fusible mate rial governing the action of themovable member of the said hood, substantially as described.

5. The combination with a thermostatic instrument provided with circuitterminals or members, one of which is expansible, of a protective hoodpassively cooperating with the said instrument and consisting of astationary member inclosing the instrument, and a movable member fusiblyconnected to the stationary member and capable of movement independentof the thermostatic instrument, substantially as described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

MORRIS MAFL'IIN.

W itncsses:

J AS. I-I. CHURCHILL, J. MURPHY.

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